1. Field of the Invention
The present invention relates to an actuator using a piezoelectric element, and a head-positioning mechanism using the actuator. More in particular, the present invention relates to an actuator using a piezoelectric element, capable of positioning with high accuracy, and a head-positioning mechanism using such an actuator.
2. Description of the Related Art
In recent years, information equipment has increased in precision and demand has risen for an actuator able to operate over a minuscule distance. Actuators for correcting the focal point or controlling the inclination angle of optical systems or head actuators for printers and magnetic disk drives, for example, require the capability of controlling the motion thereof to a very high accuracy.
A magnetic disk drive is one of key devices of in multimedia equipment, the market for which has expanded in recent years. Development of a device having a larger memory capacity is desired for use with multimedia equipment which can handle image and voice data in a greater amount and at higher speed. An increased capacity of a magnetic disk drive is generally realized by increasing the storage capacity of each disk. If the storage density is sharply increased without changing the disk diameter, however, the track pitch is sharply reduced. The resulting technical problem is how to accurately position the head device for reading from and writing onto a recording track. A head actuator having a high positioning accuracy is therefore desired.
With conventional magnetic disk drives, an attempt has been made to improve the rigidity of the movable parts such as the carriage and thus to increase the main resonance frequency of in-plane mode. Nevertheless, increasing the frequency of the resonance frequency has its own limitation. Even if the frequency of the resonance frequency caused by stiffness of carriage arms can be increased remarkably, resonance would be generated by the spring characteristics of the bearing supporting the movable parts. Thus, it is difficult to reduce positioning errors.
Also, it has so far been difficult to increase the servo bandwidth for positioning control of a magnetic disk drive.
A proposal that has been made as a means for solving these problems is to arrange a second actuator for following the track at the forward end of the arm of the head actuator. This second actuator is capable of positioning the head at the forward end of the arm independently of the operation of the head actuator.
Unexamined Patent Publication (Kokai) No. 3-69072 (JP-A-3-69072), for example, discloses a disk drive comprising a sub-actuator, arranged at the forward end of an arm for positioning the head, in addition to a main actuator for a disk drive. This sub-actuator includes two multilayered piezoelectric elements each configured of a plurality of piezoelectric elements in the plane of head movement, each piezoelectric element being adapted to be displaced along the thickness direction. The expansion and contraction of the piezoelectric elements can move the head finely in the same direction as the plane of head movement.
This sub-actuator is formed as a swingable center spring, having the function of a spring, having a thin arm portion with a multilayered piezoelectric element arranged on both sides thereof. This swingable center spring can be configured of a plurality of slits formed alternately inwardly in the direction perpendicular to the longitudinal direction of the thin arm portion. The swingable center spring imparts a pre-load on the multilayered piezoelectric elements and enhances the operation of extension and contraction thereof at the same time. The multilayered piezoelectric elements and the arm are electrically insulated from each other by an insulating material, and lead wires are led from the electrodes at the ends thereof so that a drive voltage for the multilayered piezoelectric elements is supplied through the lead wires.
The problems of the above-mentioned conventional apparatuses are that a multilayered piezoelectric element is difficult to fabricate, that a pre-load mechanism machined with high precision is required and that the electrodes of the multilayered piezoelectric elements are required to be led out by a lead wire or a wiring member. These factors have increased the cost of the sub-actuator.
Further, the invention described in Examined Patent Publication No.2528261 discloses a head-positioning mechanism including a positioning actuator at the forward end of an arm for following the tracks. The head-positioning mechanism is mounted on a coupling plate for coupling an access arm protruded from the carriage of the head actuator to a support spring with a head mounted at the forward end thereof.
The coupling plate on which the head-positioning mechanism is arranged includes a fixed area, a movable area, an extendable area, a hinge section and a gap. A groove is formed on each of the two surfaces of the extendable area. Piezoelectric elements are fixed in the grooves. The piezoelectric elements located at symmetric positions about the center line of the coupling plate are deformed in opposite directions at the same time upon application of different potentials from a power supply to the outer side surfaces thereof, respectively, with the coupling plate as a common electrode.
The head-positioning mechanism having the above-mentioned configuration, however, requires a high accuracy in the fabrication of the multilayered piezoelectric elements and highly accurate outer dimensions of the element. Further, the arm is required to be machined with high dimensional accuracy and the coupling plate having a comparatively high rigidity is required to be extended and contracted. The resulting problem is that strong forces are required to obtain a predetermined stroke in the head-positioning mechanism.
The object of the present invention is to provide an actuator using a shear-type piezoelectric element capable of positioning a head transducer with high accuracy without requiring a high dimensional accuracy of component parts and a head-positioning mechanism using such an actuator.
According to a first aspect of the invention, there is provided an actuator using a shear-type piezoelectric element comprising two electrodes arranged in juxtaposition at a fixed end of the actuator, a shear-type piezoelectric element laid on the two electrodes, and an opposite electrode arranged on the surface at a free end of the actuator in an opposed relationship to the two electrodes of the shear-type piezoelectric element, wherein the opposed electrode is displaced in a direction in the plane thereof in accordance with the direction of polarization of the piezoelectric element upon application of a voltage between the two electrodes.
According to a second aspect of the invention, there is provided an actuator of the first aspect, wherein the shear-type piezoelectric element is polarized in the direction parallel to the direction in which the two electrodes are juxtaposed and wherein the shear-type piezoelectric element is displaced in such a direction as to rotate about the central portion thereof upon application of a voltage to the two electrodes.
According to a third aspect of the invention, there is provided an actuator of the first aspect, wherein the shear-type piezoelectric element is polarized in the direction parallel to the direction in which the two electrodes are juxtaposed, wherein the shear-type piezoelectric elements on the two portions of the shear-type piezoelectric elements are polarized in opposite directions to each other, and wherein the actuator is displaced in the direction parallel to the direction of polarization of the shear-type piezoelectric elements upon application of a voltage to the two electrodes.
According to a fourth aspect of the invention, there is provided an actuator of the first aspect, wherein the shear-type piezoelectric element is polarized in the direction perpendicular to the direction in which the two electrodes are juxtaposed, wherein the two portions of the shear-type piezoelectric element arranged on the two electrodes are polarized in the directions opposite to each other, and wherein the actuator is displaced in the direction parallel to the directions in which the shear-type piezoelectric element is polarized upon application of a voltage to the two electrodes.
According to a fifth aspect of the invention, there is provided an actuator of any of the first to fourth aspects, wherein a shear-type piezoelectric element is divided into two independent portions laid on two electrodes, respectively.
According to a sixth aspect of the invention, there is provided a disk drive comprising at least a recording disk, a head, and a head actuator for setting the head in position on the desired track on the recording disk, wherein a head-positioning mechanism is configured using an actuator of any of the first to fifth aspects in a part of the head actuator for moving the head by a small distance independently of the motion of the head actuator, wherein the two electrodes of the actuator are arranged at the forward end of an arm of the head actuator and wherein the base of a support spring of the head actuator is mounted on an opposed electrode of the actuator.
According to a seventh aspect of the invention, there is provided an actuator of a sixth aspect, wherein a dividing plane between the two electrodes is arranged longitudinally on the arm.
According to an eighth aspect of the invention, there is provided a disk drive of the sixth aspect, wherein the a dividing plane between the two electrodes is arranged in the direction perpendicular to the longitudinal direction of the arm.
According to a ninth aspect of the invention, there is provided an actuator using a shear-type piezoelectric element comprising a circular aperture of a predetermined depth formed at a fixed end of the actuator, two electrodes arranged in such positions on the inner peripheral surface of the circular aperture as to divide the particular inner peripheral surface into two laterally symmetric sections, two semi-annular shear-type piezoelectric elements of a predetermined thickness laid on the inner peripheral surfaces of the two electrodes and adapted to be polarized symmetrically about the dividing plane, an opposed electrode arranged over the inner peripheral surfaces of the two semi-annular shear-type piezoelectric elements, and a rotational shaft fixedly secured to the inner peripheral surface of the opposed electrode and adapted to rotate upon application of a voltage between the two electrodes.
According to a tenth aspect of the invention, there is provided a disk drive comprising at least a recording disk, a head, and a head actuator for positioning the head on the desired recording track on the recording disk, wherein a head-positioning mechanism is configured using the actuator of the ninth aspect with a part of the head actuator in order to move the head by a small distance independently of the motion of the head actuator, wherein a fixed end of the actuator is arranged at the forward end of the arm of the head actuator and wherein a movable part of the actuator is mounted on the base of a support spring of the head actuator.
According to an 11th aspect of the invention, there is provided an actuator using a shear-type piezoelectric element, comprising a deep slit-like groove of a predetermined depth formed at a fixed end of the actuator, two electrodes arranged on the two opposed internal surfaces of the slit-like deep groove, two shear-type piezoelectric elements of a predetermined thickness laid on the two electrodes, respectively, and a conductive movable plate fixedly inserted in the space between the two shear-type piezoelectric elements, wherein the movable plate is displaced in accordance with the direction of polarization of the shear-type piezoelectric elements upon application of a voltage between the two electrodes and the movable plate.
According to a 12th aspect of the invention, there is provided a disk drive comprising at least a recording disk, a head, and a head actuator for positioning the head on the desired recording track on the recording disk, wherein a head-positioning mechanism is configured using the actuator of the 11th aspect of the invention with a part of the head actuator for moving the head by a small distance independently of the motion of the head actuator, wherein a fixed end of the actuator constitutes the forward end of the arm of the head actuator and wherein the movable plate of the actuator constitutes the base of a support spring of the head actuator.
According to a 13th aspect of the invention, there is provided a disk drive comprising at least a recording disk, a head, and a head actuator for positioning the head on the desired recording track on the recording disk, wherein a head-positioning mechanism is configured using the actuator in any of the first to fifth aspects of the invention with a part of the head actuator for moving the head by a small distance independently of the motion of the head actuator, wherein the two electrodes of the actuator are arranged at the forward end of the support spring of the head actuator, and wherein a head slider of the head actuator is arranged on the opposed electrode of the actuator.
According to a 14th aspect of the invention, there is provided a disk drive in the 13th aspect of the invention, wherein the two electrodes are arranged in juxtaposition longitudinally on the support spring.
According to a 15th aspect of the invention, there is provided an actuator in the 13th aspect of the invention, wherein the two electrodes are arranged in juxtaposition in the direction perpendicular to the longitudinal direction of the support spring.
According to a 16th aspect of the invention, there is provided a disk drive comprising at least a recording disk, a head, and a head actuator for positioning the head on the desired recording track on the recording disk, wherein a head-positioning mechanism is configured using the actuator in the fourth aspect of the invention with a part of the head actuator for moving the head by a small distance independently of the motion of the head actuator, wherein the two electrodes of the actuator are arranged at an end of the head slider nearer to the head, and wherein a head element board including the head of the head actuator is arranged on the opposed electrode of the actuator.
According to a 17th aspect of the invention, there is provided an actuator comprising a fixed member constituting a baseboard, a drive member including a plurality of piezoelectric elements and a movable member arranged on the drive member, the actuator being activated upon application of a voltage to the two surfaces of the piezoelectric element, wherein each of the piezoelectric elements polarized in the direction perpendicular to the direction along the thickness thereof and deformed by shearing upon application of a voltage thereto, are laid one on another in alternate directions of polarization thereby to make up the drive member, and a voltage is applied between the electrodes of each of the piezoelectric elements thereby to drive the movable member in parallel to the fixed member.
According to an 18th aspect of the invention, there is provided an actuator comprising two drive members each including a piezoelectric element arranged adjacently in parallel to each other on a fixed member making up a baseboard, and a movable member arranged over the two drive members, the actuator being activated upon application of a voltage to the sides of each of the piezoelectric elements, wherein each of the piezoelectric elements is polarized and deformed by shearing in the directions perpendicular to the direction along the thickness thereof upon application of a voltage thereto, wherein the piezoelectric elements are arranged substantially parallel to each other in alternately opposite directions of polarization thereby to make up a drive member, and wherein a voltage is applied between each pair of electrodes in the same direction thereby to rotate the movable member relative to the fixed member.
According to a 19th aspect of the invention, there is provided an actuator of the 18th aspect, wherein each of the piezoelectric elements in a first layer has arranged thereon, through a common electrode, a second layer of piezoelectric elements in the same number as in the first layer polarized in the directions parallel and opposite to those of the piezoelectric elements in the first layer, respectively, and wherein the amount of rotation of the movable member relative to the fixed member is increased by applying a predetermined voltage thereto.
According to a 20th aspect of the invention, there is provided an actuator comprising a fixed member constituting a baseboard, a drive member including a piezoelectric element and a movable member arranged on the drive member, the actuator being activated by applying a voltage to the sides of the piezoelectric element, wherein the drive member includes the single piezoelectric element having different portions thereof polarized in two parallel and opposite directions, wherein the piezoelectric element is deformed by shearing upon application of a voltage thereto, and wherein the movable member is rotated relative to the fixed member upon application of a voltage between the electrodes of the piezoelectric element.
According to a 21st aspect of the invention, there is provided an actuator of the 20th aspect comprising a piezoelectric element making up a drive member, and at least a second piezoelectric element arranged on the first piezoelectric element through a common electrode and polarized in the directions parallel and opposite to that of the first piezoelectric element, wherein the amount of rotation of the movable member relative to the fixed member is increased upon application of a predetermined voltage.
According to a 22nd aspect of the invention, there is provided an actuator of the 18th, 19th, 20th or 21st aspect, wherein an electrode for applying a voltage to the side of the piezoelectric element nearer to the fixed member is arranged independently for each direction of polarization of the piezoelectric element.
According to a 23rd aspect of the invention, there is provided an actuator of the 17th, 19th or 21st aspect, wherein a plurality of the piezoelectric elements stacked one on another have a portion thereof not overlaid, and wherein the electrode portion exposed from the overlaid portion is connected with a lead wire for applying a voltage.
According to a 24th aspect of the invention, there is provided an actuator of any one of the 18th to 21st aspects, wherein the movable member includes a base directly driven by a piezoelectric element and a magnified coverage portion extended from the base, and wherein a first notch for dividing the base into two portions is formed in parallel to the direction of polarization of the drive member laid on the base.
According to a 25th aspect of the invention, there is provided an actuator of the 24th aspect, wherein second notches perpendicular to the first notch are formed in the boundary between the base and the magnified coverage portion of the movable member, and wherein hinges are formed in the portion sandwiched between the forward ends of the first and second notches.
According to a 26th aspect of the invention, there is provided an actuator comprising a fixed member constituting a baseboard, a drive member including a piezoelectric element and a movable member arranged on the fixed member, the actuator being activated by applying a voltage to the two sides of the piezoelectric element, wherein the piezoelectric element is polarized in the direction perpendicular to the direction along the thickness thereof and deformed by shearing upon application of a voltage thereto, and wherein the movable member is driven in parallel to the fixed member upon application of the voltage.
According to a 27th aspect of the invention, there is provided an actuator of any one of the 17th to 26th aspects, wherein an electrode film is formed by sputtering on each of the surfaces of the piezoelectric element in contact with an electrode.
According to a 28th aspect of the invention, there is provided an actuator of any one of the 17th to 27th aspects, wherein means for applying a voltage to the side of the piezoelectric element nearer to the fixed member and the side of the piezoelectric element nearer to the movable member constitutes a conductive adhesive.
According to a 29th aspect of the invention, there is provided a head-positioning mechanism for a disk drive comprising a recording disk, a head and a head actuator, wherein the head actuator includes a piezoelectric element according to any one of the 17th to 28th aspects for moving the head independently of the head actuator, wherein the fixed member constitutes a head arm of the head actuator, and wherein the base of a support spring with a head mounted at the forward end thereof is fixed at an end of the movable member.
According to a 30th aspect of the invention, there is provided a head-positioning mechanism for a disk drive comprising a recording disk, a head and a head actuator, wherein the head actuator includes a head actuator according to any of the 17th or 28th aspects for moving the head independently of the head actuator, wherein the fixed member constitutes an access arm of the head actuator and wherein the movable member constitutes a support spring with a head mounted at the forward end thereof.
According to a 31st aspect of the invention, there is provided a head-positioning mechanism for a disk drive comprising a recording disk, a head and a head actuator, using an actuator of the 24th or 25th aspect as a part of the head actuator for moving the head independently of the head actuator, wherein the fixed member constitutes an access arm of the head actuator, wherein two electrodes are arranged in juxtaposition at the forward end of the fixed member for applying a voltage to drive members, wherein the drive members are polarized in the same direction, and wherein the base of a support spring with a head mounted at the forward end thereof is fixed at an end of a magnified coverage portion.
According to a 32nd aspect of the invention, there is provided a head-positioning mechanism for a disk drive comprising a recording disk, a head and a head actuator, using an actuator of the 24th or 25th aspect as a part of the head actuator for moving the head independently of the head actuator, wherein the fixed member constitutes an access arm of the head actuator, wherein two electrodes are arranged in juxtaposition at the forward end of the fixed member for applying a voltage to drive members, wherein the drive members are polarized in the same direction, and wherein the movable member constitutes a support spring with a head mounted at the forward end thereof.
According to the first to fifth aspects, the ninth aspect and the 11th aspect of the invention, an inexpensive and high-accuracy actuator is obtained.
According to the sixth to eighth aspects and the 13th aspect of the invention, an inexpensive and high-accuracy head-positioning mechanism is obtained using any of the actuators in the first to fifth aspects.
According to the tenth aspect, an inexpensive and high-accuracy head-positioning mechanism is obtained using the actuator of the ninth aspect of the invention.
According to the 12th aspect, an inexpensive and high-accuracy head-positioning mechanism is obtained using the actuator of the 11th aspect of the invention.
According to the 14th and 15th aspects, an inexpensive and high-accuracy head-positioning mechanism is obtained using the actuator of the 13th aspect of invention.
According to the 16th aspect, an inexpensive and high-accuracy head-positioning mechanism is obtained using the actuator of the fourth aspect of the invention.
According to the 17th aspect, the movable member can be driven in parallel to the fixed member, so that a parallel-driven actuator is obtained which is large in displacement, inexpensive and high in precision.
According to the 18th aspect, the movable member can be rotated relative to the fixed member, so that a rotary actuator is obtained which is inexpensive and high in precision.
According to the 19th aspect, the amount of rotation of the movable member relative to that of the fixed member can be increased.
According to the 20th aspect, the movable member can be rotated relative to the fixed member, and a rotary actuator is obtained which is composed of a smaller number of parts, is inexpensive and is high in precision.
According to the 21st aspect, the amount of rotation of the movable member relative to the fixed member of the actuator according to the 20th aspect can be increased.
According to the 22nd aspect, the movable member can constitute a common electrode and therefore is not required to be connected to one of electrodes.
According to the 23rd aspect, a lead wire for applying a voltage can be connected to an exposed portion of a plurality of piezoelectric elements having different sizes formed one on another in an actuator according to the 17th or 19th aspect, so that the lead wire can be easily connected to an intermediate electrode.
According to the 24th aspect, a first notch is added to an actuator according to any one of the 18th to 21st aspects, so that the device can be deformed to a greater extent to thereby secure a larger distance coverage by the magnified coverage portion.
According to the 25th aspect, second notches are added to the actuator according to the 24th aspect to form a hinge structure, thereby securing an even greater distance coverage by the magnified coverage portion.
According to the 26th aspect, an actuator having a simple and basic configuration is obtained.
According to the 27th and 28th aspects, the contact between the piezoelectric element and the electrodes is improved so that the piezoelectric element extends and contracts efficiently.
According to the 29th to 32nd aspects, the fixed member of the actuator according to the 17th to 28th aspects constitutes an access arm of the head actuator, thereby providing a head-positioning mechanism which is inexpensive, superior in production efficiency, smaller in the number of parts and high in precision.